Rubber flooring or sheeting



Patented June 30, 1942 RUBBER FLOORING OR, SHEETING Carroll 0. Davis,Belmont, Mass., assignor to 1305- ton Woven Hose & Rubber Company,Cambridge, Mass, a corporation of Massachusetts No Drawing. ApplicationMarch 15, 1940,

Serial No. 324,121

1 Claim.

This invention relates to rubber material adapted for use as flooring orrubber sheeting and in One aspect consists of rubber sheet materialhaving a novel composition to render it electrocon'ductive together withother desirable characteristics.

A very serious condition exists in operating rooms of hospitals onaccount of the extremely explosive nature of certain modern anestheticsand the danger of their ignition by electrostatic discharges. Manyoperating rooms have been equipped With various types of floors havinghigh insulating characteristics. In working and walking about on suchfloors, surgeons and nurses are likely to accumulate a charge of staticelectricity, which, on being discharged through contact with anotherperson or article in the room, is often sufficient to ignite anycombustible vapor present in the air of the room or in the lungs of thepatient. Disastrcus and fatal explosions of this kind have occurred inthe past under the conditions described, and not only in operating roomsbut in laboratories and factories where explosive mixtures of air andvapor have been formed.

My improved flooring is particularly adapted for use in factories,shops, hospitals, and like places which especially require the featuresabove referred to and hereinafter described. One essential requirementfor many of such uses is that the flooring shall be non-productive ofsparks which may cause injurious explosions and the improved flooring isconstructed to fulfill this requirement to a high degree andat the sametime meet the other necessary requirements. These other requirementsinclude a flexibility and resilience providing a quiet and easy treadingsurface and a flooring sheet capable of being bent and rolled withoutcracking and resiliently firm and hard to a degree precluding permanentindentation in use. The composition of my improved flooring isfurthermore such that other desirable characteristics possessed by knownflooring, such as the presenting of an attractive surface appearance,are not lost or sacrificed. The production of an improved flooringembodying a novel combination of these desirable features comprises theprimary object of the invention.

The electrical resistivity of the present known commercial fioorlngs isextremely high, running into millions of ohms per centimeter cube. In

contrast to such resistivity characteristics, the present inventioncontemplates a resistivity of not more than 20,000 ohms per centimetercube. In practice, it has been found possible to reduce the resistivityof my improved flooring to approximately 1,200 per centimeter cube. Itwill be apparent that this flooring provides such a grounding forpersons and objects in contact with it as immediately to dissipatedangerous static charges that might otherwise exist or be generated bysending or other frictional movement.

While not essential, it is highly desirable to incorporate with thesheet material a ply of metal screen wire such as copper or brass of 12to 24 mesh or thereabouts. The screen wire acts as a reinforcing elementand a rigid skeleton to prevent the sheet material from stretching andbuckling. It also greatly improves the conductance of the compositesheet. It is important that the screen wire should not be lacquered butshould present a bare uncoated metal for intimate conductive contactwith the composition of the rubber sheet material whereby to render thesheet uniformly highly conductive from any point on its surface.

As a result of most careful and extended research, I have discoveredthat a satisfactory electroconductive rubber or rubber-like sheetmaterial may be compounded of smoked sheet rubher, with advantageousproportions of graphite in flake or powdered form, carbon black, sulfur,activating agent, dispersing agents and antioxidant. One satisfactoryformula is as follows:

\ Parts by weight Smoked sheet rubber 23 Graphite 59 Thermax'black 12Pine tar 2% Zing mrirlp 1f Stearic acid Sulfur it Benzothiazyl disulfldeA Mixed polymers of 2,2,4-trimethyi-L2-hydroquinoline V .cube.

mixture of the above formula is calendered, and cured to the desiredthickness by the usual steps of, commercial processing, which need noelaboration here, since they are well known and understeed by thoseskilled in the art. The resulting sheet material does not crack whenbent, has sufiicient resilient hardness or firmness to resistindentation during service, and has an electrical resistivity of 1,200to 2,400 ohms per centimeter j I Parts by weight Smoked sheet rubber 100Graphite 300 Zinc oxide- Stearic acid Sulfur Paramn wax Benzothiazyldisulfide Vulcanized sheet material produced from this formula does notcrack when bent, has sufficient resilient hardness or firmness to resistindentatiorr and a resistivity of 2,000 ohms per centimeter cube. Inthis formula the stearic ,acid and paraflin wax are bothsofteningingredients.

I have found that a mixture of graphite and of commercial carbon blacks,such as Thermax and Fumonex, gives higher electrical conductiv- Anothersatisfactory formula ity than graphite alone, and that these blacks alsoincrease resistance to wear. v

z I have given two typical and satisfactory formulas and from these itwill be evident that the proportion by weight of graphite should be atleast twice that of rubber and that, whereas the addition of acommercial black is desirable, it is not essential. Furthermore, it ispossible, and perhaps advantageous under some conditions, to substituteNeoprene for natural rubber. An illustrative formula using Neoprene isas follows:

enemas Parts by weight Neoprene G 100 Light magnesium oxide 4 Zinc oxide6 Soy bean oil 10 Mineral oil 10 Stearic acid V2 Paraiiln Graphite(powdered) 200 In general, powdered graphite is preferred for thegraphite ingredient of the formula, although flaked graphite may besubstituted with setbfactory results if more convenient. In this formulathe soy bean oil, mineral oil, stearic acid and paraflln are softeningingredients.

Flooring compounded in accordance with any of the formulas abovesuggested has a conductivity of an order of magnitude of about 1.0 mhoper square foot between the surface of the flooring and the conductivewire screen. Actually flooring has been made with a conductivity as highas 4.0 mhos per square foot between the surface of the flooring and theelectrically conductive wire screen. These values refer to floor ingwith a layer of rubber approximately 0.06.25 inch on top of the wirescreen. In service,

therefore, the material has little or no insulating effect, andaccumulation of static charges does not occur to any detectable extent.

.In the following claims the term "rubber ingredient is used to includewithin its scope natural rubber, artificial or synthetic rubber, andrubber-like materials, such as Neoprene.

1 Having thus disclosed my invention and speclflcally described certainspecific embodiments thereof for purposes of illustration, but not byway of limitation, I claim as new and desire to secure by LettersPatent:

A rubber-like electro-conductive flooring sub-I stantially of thefollowing composition processed to a homogeneous mass and shaped insheet form and vulcanized to provide flooring sufliciently flexible andresilient to form a quiet and easy treading surface and capable of beingbent and .rolled without cracking and resiliently firm and hard to adegree precluding permanent indentation in use: r

- Approx. parts by weight CARROLL 0. Davis.

